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Vapour lock? Why?
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frans(at)privatepilots.nl
Guest

Posted: Mon Jul 30, 2012 2:05 am Post subject: Vapour lock? Why?

Hi everyone,



Just returned from a trip to the French Alps.



I have had some worrying experience, so I hope to gain some wisdom from

the group.



What happened is that during the take off roll from a 4000ft altitude

field on a hot day, the engine hesistated and didn't develop full power.

As it was a rather short runway in a valley with absolutely no suitable

fields in the proximity for an emergency landing I aborted the take off

(and was happy it happened early in the take off roll).



Associated with the drop of power I saw the fuel pressure drop (note a

recent discussion where I discussed the importance to have a

conventional fuel pressure gauge at the top of the panel, as an unusual

swing of a needle surely catches your attention). A quick check of the

fuel system didn't indicate any abnormalities. Idle and medium power was

ok, but at full power the fuel pressure dropped everytime. My conclusion

was that it had to be vapour lock in some way, so I decided to try

another day in the morning. Indeed the problem appeared to have solved

itself and ground runs gave enough confidence to attempt a take off. The

engine developed full power as it usually does and the 4.5 hour flight

home was just like normal.



I don't fully understand how this could happen however. I have taken off

in hotter weather.



My assumption so far is that it happened because of the combination of

altitude and temperature, and the fact that I refueled the airplane in

the morning while the take off was in the afternoon and the fuel had

plenty of time to heat up while the airplane was parked in the sun.

Another difference was that the floor of the bagage bay was now covered

with a black piece of carpet instead of the white carpet I normally have.



A few questions here:

1) Is there any difference it the type of fuel (AVGAS, MOGAS) regarding

to the sensitivity to vapour lock?

2) Is there anything that can be done about it? (I assume that it must

have occured at the fuel pump inlet, under the bagage bay).

3) My habit is to switch on the second fuel pump while lining up. Maybe

it is better to switch on the second fuel pump earlier? (This second

fuel pump is also used for starting the engine, so it had already run.

After startup I switch fuel pumps, so before lining up both pumps have

already ran and found to be ok, and should have been "cooled" by the fuel).

4) Will a cockpit cover help? (Maybe the answer is obvious, but I'm

hoping to hear from someone that the very same problem was cured by

using a cockpit cover).

5) Is my conclusion and assumption about the vapour lock correct, or do

I need to investigate further?



Thanks,

Frans

Rocketman

Joined: 07 Sep 2010
Posts: 87
Location: USA, Earth

Posted: Mon Jul 30, 2012 5:47 am Post subject: Vapour lock? Why?

Frans,



My own experience with vapor lock was nerve wracking. After fighting it 

for months, I finally figured it out. The carb bowls were getting hot.



Check your exhaust for a good seal and build a baffle to fit behind and 

inside on the rear exhaust down tubes.  These will deflect the hot air 

away from the carbs.  I also fire sleeved all exposed fuel lines, under 

the cowl.  Worked for me.  Zero problems since.



Jeff - Baby Blue



On 7/30/2012 5:58 AM, Frans Veldman wrote:

 	  Quote: 	
		   



 Hi everyone,



 Just returned from a trip to the French Alps.



 I have had some worrying experience, so I hope to gain some wisdom from

 the group.



 What happened is that during the take off roll from a 4000ft altitude

 field on a hot day, the engine hesistated and didn't develop full power.

 As it was a rather short runway in a valley with absolutely no suitable

 fields in the proximity for an emergency landing I aborted the take off

 (and was happy it happened early in the take off roll).



 Associated with the drop of power I saw the fuel pressure drop (note a

 recent discussion where I discussed the importance to have a

 conventional fuel pressure gauge at the top of the panel, as an unusual

 swing of a needle surely catches your attention). A quick check of the

 fuel system didn't indicate any abnormalities. Idle and medium power was

 ok, but at full power the fuel pressure dropped everytime. My conclusion

 was that it had to be vapour lock in some way, so I decided to try

 another day in the morning. Indeed the problem appeared to have solved

 itself and ground runs gave enough confidence to attempt a take off. The

 engine developed full power as it usually does and the 4.5 hour flight

 home was just like normal.



 I don't fully understand how this could happen however. I have taken off

 in hotter weather.



 My assumption so far is that it happened because of the combination of

 altitude and temperature, and the fact that I refueled the airplane in

 the morning while the take off was in the afternoon and the fuel had

 plenty of time to heat up while the airplane was parked in the sun.

 Another difference was that the floor of the bagage bay was now covered

 with a black piece of carpet instead of the white carpet I normally have.



 A few questions here:

 1) Is there any difference it the type of fuel (AVGAS, MOGAS) regarding

 to the sensitivity to vapour lock?

 2) Is there anything that can be done about it? (I assume that it must

 have occured at the fuel pump inlet, under the bagage bay).

 3) My habit is to switch on the second fuel pump while lining up. Maybe

 it is better to switch on the second fuel pump earlier? (This second

 fuel pump is also used for starting the engine, so it had already run.

 After startup I switch fuel pumps, so before lining up both pumps have

 already ran and found to be ok, and should have been "cooled" by the fuel).

 4) Will a cockpit cover help? (Maybe the answer is obvious, but I'm

 hoping to hear from someone that the very same problem was cured by

 using a cockpit cover).

 5) Is my conclusion and assumption about the vapour lock correct, or do

 I need to investigate further?



 Thanks,

 Frans



 -----

 No virus found in this message.

 Checked by AVG - www.avg.com

frans(at)privatepilots.nl
Guest

Posted: Mon Jul 30, 2012 6:12 am Post subject: Vapour lock? Why?

Jeff,



 	  Quote: 	
		   My own experience with vapor lock was nerve wracking. After fighting it

 for months, I finally figured it out. The carb bowls were getting hot.


	


This is not the problem I have. The engine was still relatively cold,

and I saw the fuel pressure drop. The fuel pressure is measured before

the carbs. A vapor lock inside the carbs doesn't result in a pressure

drop before the carbs.



I also got some private mails, but not everyone seems to know that I

have a Rotax 914. The 914 has two electrical pumps, mounted under the

bagage bay. If there is a fuel pressure drop, something is wrong outside

of the engine bay (unless it is the fuel pressure regulator itself).



I appreciate your advice, but I don't think it applies to my ship. It

can't have been the carbs.



Frans

bill.sue(at)orcon.net.nz
Guest

Posted: Mon Jul 30, 2012 8:25 pm Post subject: Vapour lock? Why?

Have you checked the finger filter in the entry side of the fuel pump?

Cheers

Sue & Bill

On 31/07/2012 3:05 a.m., Frans Veldman wrote:

 	  Quote: 	

 Jeff,

> My own experience with vapor lock was nerve wracking. After fighting it

> for months, I finally figured it out. The carb bowls were getting hot.

 This is not the problem I have. The engine was still relatively cold,

 and I saw the fuel pressure drop. The fuel pressure is measured before

 the carbs. A vapor lock inside the carbs doesn't result in a pressure

 drop before the carbs.

 I also got some private mails, but not everyone seems to know that I

 have a Rotax 914. The 914 has two electrical pumps, mounted under the

 bagage bay. If there is a fuel pressure drop, something is wrong outside

 of the engine bay (unless it is the fuel pressure regulator itself).

 I appreciate your advice, but I don't think it applies to my ship. It

 can't have been the carbs.

 Frans

frans(at)privatepilots.nl
Guest

Posted: Mon Jul 30, 2012 11:41 pm Post subject: Vapour lock? Why?

On 07/31/2012 06:24 AM, Bill Sisley wrote:



 	  Quote: 	
		   Have you checked the finger filter in the entry side of the fuel pump?


	


Good point. I didn't.



Since home I have digged deeper into this subject. I didn't mention that

I topped off the tank with 40 liters of mogas. I just assumed that apart

from the ethanol and lower octane rating and absence of lead that the

fuel would have a similar boiling point. I now learned that this

assumption is totally wrong. Given the altitude and temperature it is

fully understandable that I experienced vapor lock, mogas just has to

vaporize in these conditions.



So, this is a lesson learned. I should have learned more about it

instead of blindly pouring in mogas because it is best for the engine

and so far always worked very well.



Which now poses a dilemma. I try to avoid using avgas as much as

possible because of the lead. But now I should try to avoid using mogas

when the temperatures are high and the altitude is high. Given my

personal preferences regarding weather and flying altitude this applies

to most of the longer trips.



It looks like the vapour lock develops at the inlets of the electrical

fuel pumps. The fuel has to be sucked through the fuel filters and this

drop in pressure causes formation of bubbles. I have actually observed

this happening when I was building the airplane and put the fuel system

in use on a hot day: I spent a lot of time searching for a supposed air

leak because of all the bubbles I saw passing the fuel filters, which in

the end turned out to be "just" fuel vapor bubbles.



Reading more about this subject I have learned that the best way to

prevent this from happening is to put a fuel pump *inside* the fuel tank

to get the pressure up before the fuel even leaves the tank, and not to

suck fuel through the filter but to push it through the filter. This way

one prevents the pressure drop which causes the fuel to vaporize.

It seems that this is a common practice in cars with fuel injection, to

have the fuel pump literally inside the tank or at least directly at the

tank outlet.



Of course such a fuel pump could fail (especially because it lacks a

fine filter before the inlet) so it is an additional risk. Then again it

is possible to use it only on one of the fuel tank outlets. Switching to

the other outlet then bypasses the failed pump.



I now just wonder how many of us are actually using mogas in hot

weather? Am I the only one struggling with this dilemma?



Frans

rparigoris

Joined: 24 Nov 2009
Posts: 805

Posted: Tue Jul 31, 2012 12:32 am Post subject: Vapour lock? Why?

Hi Frans 

 	I have a 914, not flying yet. I purchased a tool from the guy who makes the lead scrubber additive (not TCP, the one not for use with certified aeroplanes, but you can transport in cabin) that measures at what altitude you can fly to with the brew in your fuel tank. It takes into consideration temp, % of avgas, % of mogas and % of alcohol. It's a syringe that you pull a specific vacuum on a scale, let it sit for a short time and you can read then to what altitude you are safe to fly to. It is very possible on a hot day at a high temperature, you get a stay on the ground reading. I noticed he stopped selling them a while back though. 

 	That said, do you have a differential pressure gauge on your 914? Direct fuel pressure reading does not provide very useful info unless you do the calculations to see how you are doing. Did you do the math to determine if you are in the differential limits? 

 	It's worth it to do I think it's in Europas test, cheat your fuel pressure regulator to thinking you are at ~ 18K (I think that was the approx. test), then do a fuel flow test, monitor differential fuel pressure as well and make sure you are where you want to be. The thinner the outside air and the thicker (inside your engine MP) air, the more fuel pressure you will need. Something marginal will usually show itself at this time. A restriction in your fuel system will also show. Do you have a single point of failure or restriction in your system like a gasculator? Or do you have a system when you turn on pump #2 it sucks from a separate fuel filter? What happened when you turned on pump two, did it not make a change? Rotax recommends cleaning the fuel pump intake side filter socks once a year, they say that this is the leading cause of fuel pump failures. 

 	On a 914 the float bowl gasket sealing is critical, differential fuel pressure being positive only means you will be able to force the fuel into the float bowls, if there is not airbox pressure that is maintained in the float chamber (or higher than airbox pressure in the case you are asking more than 108% power and the hand in the breeze is plumbed into) your carbs with be providing a serious lean mixture condition. 

 	If you are flying out of a tight field with a 914, if you are asking more than what a 912 can produce it's prudent to follow Rotax 914 users manual and do a DO, I forget if it's a 178 or something in the 170s take off. In other words turn off the TCU with the wastegate in the closed position and adjust you MP with the throttle. Once you reach a safe altitude then turn back on the TCU, this prevents the TCU for whatever reason from turning the 914 into a straight 912 at just the wrong moment. 

 	For a short period of time using the throttle to control MP is not going to cause much harm, but doing this trick for long periods of time is bad for the turbo, the turbo is working overtime and you are now forcing it's cool side output into a restriction. 

 	I don't know if your mogas has alcohol in it, but flying up high and into colder conditions can make the alcohol that has commingled with water to precipitate out and cause problems. I for one will probably follow my vapor pressure tools suggestion, and if I plan on flying high will add 2 or 3% Isopropyl Alcohol to my mix in an attempt to keep water in solution. The more alcohol you run the richer your mixture needs to be. I will make sure when I do the required by Rotax (but not many folks do this great test) CO test to make sure your leanest cylinder is running rich enough at War Emergency power (I will also test between 85 and 100% too), I will do this with 10% Ethanol and 5% Isopropyl. I am installing the ability to lean along with an O2 sensor driven display to see how the mixture is doing in addition to EGTs. 

 	Ron P.    [quote][b]

frans(at)privatepilots.nl
Guest

Posted: Tue Jul 31, 2012 1:26 am Post subject: Vapour lock? Why?

Hi Ron,



 	  Quote: 	
		   I have a 914, not flying yet. I purchased a tool from the guy who makes

 the lead scrubber additive (not TCP, the one not for use with certified

 aeroplanes, but you can transport in cabin)


	


Decalin?



 	  Quote: 	
		   that measures at what

 altitude you can fly to with the brew in your fuel tank. It takes into

 consideration temp, % of avgas, % of mogas and % of alcohol. It's a

 syringe that you pull a specific vacuum on a scale,


	


Hey, great idea!

An easy way to do this is to measure the pressure drop inside the

suction line (fuel pump inlet, downstream fuel filters) (you have to

measure this only once, preferably on fuel filters at the end of their

life) and pull this amount of vacuum on your fuel sample and see if it

starts to "boil" in that condition. If you take a sample of the fuel in

the tank, you already have the correct temperature and %avgas and

altitude applying to your situation.



I could even make a built in device that does so automatically and

registers whether bubbles develop, and gives an alarm.



Or, even much more simple: install a piece of glas in the fuel line (the

standard Europa fuel filter with its internals removed will do) and

detect if any bubbles are passing. It could give an instant alarm when

bubbles are detected "Vapor lock! Vapor lock!". Just as with boiling

water, micro bubbles will start forming some time before hell turns loose.

Regardless of changing circumstances (altitude, throttle setting, fuel

temperature) it would instantly alert for dangerous conditions.



 	  Quote: 	
		   That said, do you have a differential pressure gauge on your 914?


	


Yep. I'm one of the guys stressing the importance of such a gauge.



 	  Quote: 	
		   Do you

 have a single point of failure or restriction in your system like a

 gasculator?


	


No, I have two filters, each connected to one fuel pump.



 	  Quote: 	
		   What happened when you turned on pump two,

 did it not make a change?


	


I had already two pumps on when it happened, but I think that one pump

had performed better in this situation due to the lower pressure drop

over the fuel filter.



 	  Quote: 	
		   I don't know if your mogas has alcohol in it, but flying up high and

 into colder conditions can make the alcohol that has commingled with

 water to precipitate out and cause problems.


	


I only buy fresh mogas and pour it in just before flight.



 	  Quote: 	
		   I will make sure when I do the required by Rotax (but not many folks

 do this great test) CO test to make sure your leanest cylinder is

 running rich enough at War Emergency power (I will also test between 85

 and 100% too),


	


I plan on installing an injection system this winter, to get rid of the

carbs, and getting the correct mixture in all cylinders all the time.



Frans

JonSmith

Joined: 21 May 2010
Posts: 110

Posted: Tue Jul 31, 2012 1:32 am Post subject: Re: Vapour lock? Why?

Hi Frans,  Just for interest - the UK LAA's website contains some useful info on Mogas and the LAA requirements. It's under the tab "LAA aircraft" and sub tab "Mogas". There's general requirements for all LAA aircraft (that wish to use Mogas) plus some specific requirements for particular types, ie Rotaxes, Europas etc.  Amongst other things, each individual aircraft has to be approved, placcarded and signed off by an inspector to use Mogas, we have to have fuel return lines, fuel drains etc etc..



There is a lot of emphasis on the volatility of Mogas compared to Avgas and we must only use BS EN228 95 RON and the mandatory operating limitations are specified as a maximum altitude of 6000 feet and a maximum fuel temperature of 20 deg C.  



I have only experienced one episode of vapour locking on my Europa (912ULS).   In the UK it seems to be impossible now to obtain ethanol-free mogas (we are not approved to use it if it does contain ethanol). My local garage sells the higher octane "excellium" grade (98 RON) which I tested to be ethanol free.  My completely uneducated thinking at the time said - sounds good stuff - that will be great!  I did not know at the time that this fuel is also completely not authorised for use as Mogas due to its (even) higher volatility, according to the LAA notes.  I used it 3 or 4 times with no probs until one day, after a long taxy back through long grass where the engine got quite warm I tried to start it again after a few minutes and it just would not fire at all.  After a few attempts there was a very strong smell of fuel and I could hear it boiling.  So I left it for a couple of hours with the cowl off and later it bust into life at the first go!



Now I try to use the new 91UL where possible.

Cheers,

_________________
G-TERN
Classic Mono

rparigoris

Joined: 24 Nov 2009
Posts: 805

Posted: Tue Jul 31, 2012 2:42 am Post subject: Vapour lock? Why?

Hi Frans 

 	It was Decalin, I just did a quick search and found a pretty good article you may want to read, it has the fuel tester on the bottom with the name of the place that sells it, I don't know if they still do.: 

 	http://www.eaa.org/autofuel/autogas/articles/1Autogas%20vs%20Avgas.pdf 

 	Fresh mogas can have a lot of water already attached to the alcohol that you will never see or know about until you fly in thinner and colder air. 

 	I did quite a bit of fooling with my fuel system in controlled conditions and was very surprised at all the bubbling going on, it was at sea level, room temp and 100LL, see: 

 	http://contrails.free.fr/engine_914_fuel_syst_test_en.php 

 	Here's some information about my 914 fuel system: 

 	http://www.europaowners.org/main.php?g2_itemId=28612 

 	Download and read about the 914 fuelpump pre filter. 

 	Did you check the vent for your fuel tank making sure no nasty bug clogged it up on you? 

 	Ron P.    [quote][b]

frans(at)privatepilots.nl
Guest

Posted: Tue Jul 31, 2012 3:46 am Post subject: Vapour lock? Why?

On 07/31/2012 12:41 PM, rparigor(at)suffolk.lib.ny.us wrote:



 	  Quote: 	
		   It was Decalin, I just did a quick search and found a pretty good

 article you may want to read,


	


Good article indeed!



 	  Quote: 	
		   http://contrails.free.fr/engine_914_fuel_syst_test_en.php


	


This web page mentions "air" in the filters, which should be "fuel

vapor". This is caused by the pressure drop in the fuel filters due to

the flow resistance. The fuel pumps not only increase the fuel pressure

at the output, they also decrease the fuel pressure at the inlet.

As we all (should) know, lower pressure lowers the boiling point.



So, to get rid of the bubbles, you have to prevent the pressure drop in

the fuel filter and/or pump inlet.



One way of achieving this is to install a pre-pump directly at one of

the tank outlets.



I found some interesting pumps at ebay for a low cost (35$). They have

no diaphragms or other rubber or wearable parts but just a piston pulled

by a magnetic coil. If the pump stalls it is just a go-through.

Alternatively one can make a bypass with a check valve. The pumps

deliver 5 GPH, enough for a Rotax, at a pressure of 2 PSI. The pressure

is enough to cancel out the pressure drop of the filters, valves and

hoses and pump inlet, and thus prevent the formation of bubbles (or

vapor lock in more severe cases).



Frans

paul.the.aviator(at)gmail
Guest

Posted: Tue Jul 31, 2012 4:52 am Post subject: Vapour lock? Why?

Hi All,

I don't know if this helps or not, but in 1000 hours of operation I have never experienced a vapor lock like Frans has described using Mo Gas. I have operated my aircraft on days that are 35c ~ 40c, which have included long taxi runs.  My experience may not translate because most of my take off and landings  are at around 1000' MSL.  On hot days this equates to about 3000' density altitude.

What I have seen is the engine will not start on a hot day after sitting for a while and what I do in this situation is to turn the fuel pumps off, start the engine and then turn the pumps on.

I have a single gascolator, with dual pumps + check valves in parallel and this sits under the baggage bay. I also have a UMA differential fuel pressure sensor.

Paul

On Tue, Jul 31, 2012 at 7:38 AM, Frans Veldman <frans(at)privatepilots.nl (frans(at)privatepilots.nl)> wrote:

[quote] --> Europa-List message posted by: Frans Veldman <frans(at)privatepilots.nl (frans(at)privatepilots.nl)>

On 07/31/2012 12:41 PM, rparigor(at)suffolk.lib.ny.us (rparigor(at)suffolk.lib.ny.us) wrote:

 > It was Decalin, I just did a quick search and found a pretty good

 > article you may want to read,

Good article indeed!

 > http://contrails.free.fr/engine_914_fuel_syst_test_en.php

 This web page mentions "air" in the filters, which should be "fuel

 vapor". This is caused by the pressure drop in the fuel filters due to

 the flow resistance. The fuel pumps not only increase the fuel pressure

 at the output, they also decrease the fuel pressure at the inlet.

 As we all (should) know, lower pressure lowers the boiling point.

 So, to get rid of the bubbles, you have to prevent the pressure drop in

 the fuel filter and/or pump inlet.

 One way of achieving this is to install a pre-pump directly at one of

 the tank outlets.

 I found some interesting pumps at ebay for a low cost (35$). They have

 no diaphragms or other rubber or wearable parts but just a piston pulled

 by a magnetic coil. If the pump stalls it is just a go-through.

 Alternatively one can make a bypass with a check valve. The pumps

 deliver 5 GPH, enough for a Rotax, at a pressure of 2 PSI. The pressure

 is enough to cancel out the pressure drop of the filters, valves and

 hoses and pump inlet, and thus prevent the formation of bubbles (or

 vapor lock in more severe cases).

 Frans

[b]

frans(at)privatepilots.nl
Guest

Posted: Tue Jul 31, 2012 5:31 am Post subject: Vapour lock? Why?

Hi Paul,



 	  Quote: 	
		   I don't know if this helps or not, but in 1000 hours of operation I have

 never experienced a vapor lock like Frans has described using Mo Gas. I

 have operated my aircraft on days that are 35c ~ 40c, which have

 included long taxi runs.  My experience may not translate because most

 of my take off and landings  are at around 1000' MSL.  On hot days this

 equates to about 3000' density altitude.


	


This field was on about 4000' MSL... I took off quite a few times from

this field before, using Mogas. Never had any problems until the last time.



What was/might be different than previous times:

I refueled in the morning but took off in the afternoon.

I had a black carpet on the bagage floor instead of white.

Maybe the fuel itself (although purchased at the same store) might have

had a different formula.

Maybe the fuel filter has a bit more resistance than previous times

(maybe a bit more clogged?).



There are many variables.



Anyway, this event shows that it CAN happen, despite previous positive

experiences, for whatever reason. The engine ran fine after a night

waiting, so even if there is a technical problem (partially clogged

filter) it might wait to show up until a hot and high airfield (which

tend to be the most unforgiving fields for technical problems).



I think with a few minor improvements the fuel system can be made more

mogas proof. See my other posting.



 	  Quote: 	
		   What I have seen is the engine will not start on a hot day after sitting

 for a while and what I do in this situation is to turn the fuel pumps

 off, start the engine and then turn the pumps on.


	


I now always switch the fuel pump off during the turbo cool down period,

and let the engine idle until the carbs are drawn empty (this usually

takes about 1 minute). The starting problems are gone, and I think the

carbs will stay cleaner (the fuel inside the bowls will otherwise

vaporize anyway, but then leave some solid residue behind).



Frans

rparigoris

Joined: 24 Nov 2009
Posts: 805

Posted: Tue Jul 31, 2012 6:08 am Post subject: Vapour lock? Why?

Hi Frans 

 	The "air" bubbles were indeed vaporizing 100LL. I did introduce air, by ever so slightly pushing on the quick drains mounted on the bottom of either Andair 375, WOW foam city, that was air introduction. I am very concerned when I see drain valves seeping on Europas, especially 914s. 

 	The pre-pump you are talking about would help the bubbling a little, but don't think it's needed. I tested the ability to prime with various heads and also introducing intake restriction, and was very satisfied with the results. 

 	If you are hell bent on a pre-pump, I actually have one that would work. I was planning on using it to transfer fuel. I had a fleet of 3 Volvo 740 Turbo Station Wagons (two 1992 and one 1990), I finally switched them out a few years ago. The main Bosch fuel pump would consistently fail between ~ 85 and 125K. I always stocked one. I also stocked a pre-pump that lives in the fuel tank. It's a small thing about the size of the 914 pump (I just weighed it and it's 242 grams) that is very low pressure and lots of volume taking a 12 volt input. I always checked the output of this pump when changing the main pump or filter and never had a failure. I'm not complaining because it meant dropping the fuel tank.  Anyway if you look up 1992 Volvo 740 turbo with a 2.5 liter turbo engine, then the in fuel tank pre-pump (not exactly sure what they call it) it could be a good choice. It has a slight necked down area on the OD of the the intake side of the outer case with an OD of 1.430" x .675" long, nice and smooth and looks to be very robust. If you wanted to use it inline, that would be a good area to put a piece of rubber coupler over with a clamp, then the other side could have an adapter. The output side has a.312" (5/16") hose barb. The main pump although I have tried aftermarket once when I was in a pinch, it did not fit perfectly and the wiring connections were not the same, so I stuck with the Bosch. I saw the pre-pump on special once so I bought one just in case. I suspect the one I have is aftermarket? It's in a clear plastic bag that's staples closed, on the bag (Bosch always comes in a nice graphics box and it says Bosch everywhere): 

 	3517845 

 	F/Pump in tank 

 	700 Turbo 85 - 95 

 	You may be able to cross the numbers on the pump (no Mfg. name I can see): 

 	6443270(V3517845) then under that number : C3435-2 

 	Just a quick note, both pumps ran off of a fuel pump relay, after between ~ 85K and ~ 125K they too would fail. What would happen is because solder is such a bad conductor (solder is between ~ 4 and 5% the conductivity of annealed copper 110 that has 100% conductivity) the joint that carried the high current would fracture fail from the long period cycling between cold and hot. You would get the tell tale ring that many suspect is a "cold solder joint" but in fact a fractured solder joint. Anyway the relays were cheap enough, but not cheap enough for my liking, so I kept a spare in every car (only takes a few minutes to change)  and would re-solder them every few years (all 3 at once). They came apart really easily and the contacts still looked fine so I just kept on re-soldering. I actually solder sucked out the solder that fractured, and re-flowed with model aeroplane racing solder, what racing solder is, it's a fairly low temp solder with some silver in it, so I would re-solder and suck a few times to get as much new in the joint, it holds up a little better than 63-37 or 60-40. Again getting off track, it was not possible on this joint, but if there is enough tail on whatever it is you are re-soldering to a board that failed from fracturing, if you can make a wrap of wire around the tail and solder the two ends of that wire to another part of the copper land, you will greatly reduce the chance of failure later on. On many an occasion if I had a troublesome joint, I would purchase a new component, not because the component failed, but for it's longer tail and do whatever to make more solder surface area of solder that is conducting that would prevent a lot of heating and cure the malady, or at least greatly increase the time between failures. 

 	Anyway if you do go to two pre-pumps (or even one) be cognizant that two pumps in parallel draws enough amps that over time any solder joint that may flow electrons to the two pumps could in fact be a failure point. The first time it happened to me it was a drive you crazy malady to figure. First time, didn't hear the pump working with a stuck car. Come back and it runs fine? OK replace the pump and all is well, for a week or two, then the same thing, get stuck, come back and all is well. Depending on heating and cooling the fool joint would make or break. Hard to troubleshoot, easy to fix once you know. 

 	Ron P. 

 	  

 	     [quote][b]

frans(at)privatepilots.nl
Guest

Posted: Tue Jul 31, 2012 8:14 am Post subject: Vapour lock? Why?

Hi Ron,



 	  Quote: 	
		   The pre-pump you are talking about would help the bubbling a little, but

 don't think it's needed.


	


Think about the bubbles again. Why are they there? They are not in the

tank, right? So somewhere down the line the fuel starts vaporizing. Why

is that, and how can you prevent that? This is where the pre-pump comes

in. No pressure drop = no bubbles. No bubbles = no vapour lock.



 	  Quote: 	
		   If you are hell bent on a pre-pump, I actually have one that would work.


	


It sounds interesting. I have to measure to see if it can be made to fit

the tank outlet. Also I would prefer a pump that is "open" if switched

off. This way I can only activate it when using mogas, hot and/or high,

during take off. Or I have to use an external bypass with check valve,

but for an in-tank pump this is complicated.

I will come back to this once I have made up my mind, will let you know.



 	  Quote: 	
		   Just a quick note, both pumps ran off of a fuel pump relay, after

 between ~ 85K and ~ 125K they too would fail. What would happen is


	


Fun isn't it, these modern cars? My daily driver is a 1972 Mercedes 300

SEL (V8, running on propane, all options) and it just keeps going,

almost no maintenance.  Imagine the looks of people every time I use

it to tow the Europa back and forth to the airport. Have been

photographed a lot of times. 



 	  Quote: 	
		   Anyway if you do go to two pre-pumps (or even one) be cognizant that two

 pumps in parallel draws enough amps that over time any solder joint that

 may flow electrons to the two pumps could in fact be a failure point.


	


This is why I want to make the pre-pump optional and give it its own

wiring. Also, this way I can check to see before startup that it is

working, to use it to "prime" the fuel system and get confirmation on

the gauge that it is developing some pressure.



 	  Quote: 	
		   The first time it happened to me it was a drive you crazy malady to

 figure. First time, didn't hear the pump working with a stuck car. Come

 back and it runs fine? OK replace the pump and all is well, for a week

 or two, then the same thing, get stuck, come back and all is well.

 Depending on heating and cooling the fool joint would make or break.


	


I had the same thing with the EFI of my car (yes, the good old Merc.

Well, after 40 years of service I can accept this).



Frans

klinefelter.kevin(at)gmai
Guest

Posted: Tue Jul 31, 2012 9:51 am Post subject: Vapour lock? Why?

I have the same system Paul describes. I have not experienced the problem Frans had. But I operate consistently at far higher density altitudes and temps than described.

Frans, perhaps you are on to something regarding the filters before the pumps causing vaporization of the auto fuel at high density altitude/temp, and perhaps that is the part of the system that is need of redesign. I wonder if trying larger filters and fuel lines would mean less resistance and therefor no vaporization?

Kevin

PS- it was great to see few Europa drivers at Oshkosh!

On Jul 31, 2012, at 5:51 AM, Paul McAllister <paul.the.aviator(at)gmail.com (paul.the.aviator(at)gmail.com)> wrote:

[quote]Hi All,

I don't know if this helps or not, but in 1000 hours of operation I have never experienced a vapor lock like Frans has described using Mo Gas. I have operated my aircraft on days that are 35c ~ 40c, which have included long taxi runs.  My experience may not translate because most of my take off and landings  are at around 1000' MSL.  On hot days this equates to about 3000' density altitude.

What I have seen is the engine will not start on a hot day after sitting for a while and what I do in this situation is to turn the fuel pumps off, start the engine and then turn the pumps on.

I have a single gascolator, with dual pumps + check valves in parallel and this sits under the baggage bay. I also have a UMA differential fuel pressure sensor.

Paul

On Tue, Jul 31, 2012 at 7:38 AM, Frans Veldman <frans(at)privatepilots.nl (frans(at)privatepilots.nl)> wrote:

 	  Quote: 	
		   --> Europa-List message posted by: Frans Veldman <frans(at)privatepilots.nl (frans(at)privatepilots.nl)>

On 07/31/2012 12:41 PM, rparigor(at)suffolk.lib.ny.us (rparigor(at)suffolk.lib.ny.us) wrote:

 > It was Decalin, I just did a quick search and found a pretty good

 > article you may want to read,

Good article indeed!

 > http://contrails.free.fr/engine_914_fuel_syst_test_en.php

 This web page mentions "air" in the filters, which should be "fuel

 vapor". This is caused by the pressure drop in the fuel filters due to

 the flow resistance. The fuel pumps not only increase the fuel pressure

 at the output, they also decrease the fuel pressure at the inlet.

 As we all (should) know, lower pressure lowers the boiling point.

 So, to get rid of the bubbles, you have to prevent the pressure drop in

 the fuel filter and/or pump inlet.

 One way of achieving this is to install a pre-pump directly at one of

 the tank outlets.

 I found some interesting pumps at ebay for a low cost (35$). They have

 no diaphragms or other rubber or wearable parts but just a piston pulled

 by a magnetic coil. If the pump stalls it is just a go-through.

 Alternatively one can make a bypass with a check valve. The pumps

 deliver 5 GPH, enough for a Rotax, at a pressure of 2 PSI. The pressure

 is enough to cancel out the pressure drop of the filters, valves and

 hoses and pump inlet, and thus prevent the formation of bubbles (or

 vapor lock in more severe cases).

 Frans

===================================

tp://www.matronics.com/Navigator?Europa-List

===================================

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===================================

matronics.com/contribution

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[b]

terrys(at)cisco.com
Guest

Posted: Tue Jul 31, 2012 9:59 am Post subject: Vapour lock? Why?

Hi Frans,



We had a problem with vapor lock in our XS mono-wheel with 912S, which caused the engine to run rough.  I happened several times, only in the winter months.  This happened several times on take off after a cold start of the engine, at or near sea level.  We use auto fuel, and here in the US, they put more volatiles in the fuel in the cold months to help starting.  It seemed to create a bubble of vapor at or near the carbs that would slowly (tens of minutes) go away.  On one occasion I was doing some glide tests (at about 8000 feet) with the engine shut down, when I restarted the engine it ran rough, I turned on the electric boost pump and it killed the engine completely.  What I think happened is the extra boost 'blew' the entire bubble into the carbs all at once and killed the engine.  I restarted the engine and it ran better in a few minutes.

We put aluminum coated insulation around the float bowls and nearby lines and never had the problem again.



Regards,

Terry Seaver

A135 XS

--

frans(at)privatepilots.nl
Guest

Posted: Tue Jul 31, 2012 12:04 pm Post subject: Vapour lock? Why?

On 07/31/2012 07:50 PM, klinefelter.kevin(at)gmail.com wrote:

 	  Quote: 	
		   I have the same system Paul describes. I have not experienced the

 problem Frans had. But I operate consistently at far higher density

 altitudes and temps than described.


	


This is interesting. I think I have the same system as Paul and you

(With the Andair gascolator) except that I have an additional disposabel

filter for the secondary fuel pump. We are talking here about the series

configuration, right?



 	  Quote: 	
		   Frans, perhaps you are on to something regarding the filters before the

 pumps causing vaporization of the auto fuel at high density

 altitude/temp, and perhaps that is the part of the system that is need

 of redesign.


	


Well, it could be that the fuel filters are contaminated (although I

cleaned/replaced them just 40 hours ago) causing enough restriction in

harsh conditions but not enough to cause a fuel pressure drop at lower

temps/altitudes. Or I just had a bad batch of fuel.



I will check the system thoroughly and see if I can find any abnormalities.



Frans

klinefelter.kevin(at)gmai
Guest

Posted: Tue Jul 31, 2012 1:28 pm Post subject: Vapour lock? Why?

I have an Andair mini gascolator followed by a Y splitting to Andair check valves before the pumps in parallel.

I was chatting with Rob Seaton ( of Rotech in canada) at the Rotax display in Oshkosh. He recently purchased a 914 powered Europa to use as a test vehicle for the 912iS. We were talking about fuel system design, how the new 912iS has two electric pumps like the 914 except higher pressure for the fuel injection. He said he learned how too small a fuel line and/or tortured routing can cause "cavitation" at the pumps.

I think that's the same thing, cavitation vs vapor lock? So maybe your fuel filter(s), on the suction side of the pump,are causing cavitation in the pump(s). Maybe due to the size (restriction of flow) of the filter, even if they are clean. 

I do not like the fact that I have a single point of failure in one gascolator. But if I redesign, I am going to go with less restriction, larger diameter tubing.

Kevin

On Jul 31, 2012, at 1:57 PM, Frans Veldman <frans(at)privatepilots.nl> wrote:

 	  Quote: 	

 On 07/31/2012 07:50 PM, klinefelter.kevin(at)gmail.com wrote:

> I have the same system Paul describes. I have not experienced the

> problem Frans had. But I operate consistently at far higher density

> altitudes and temps than described.

 This is interesting. I think I have the same system as Paul and you

 (With the Andair gascolator) except that I have an additional disposabel

 filter for the secondary fuel pump. We are talking here about the series

 configuration, right?

> Frans, perhaps you are on to something regarding the filters before the

> pumps causing vaporization of the auto fuel at high density

> altitude/temp, and perhaps that is the part of the system that is need

> of redesign.

 Well, it could be that the fuel filters are contaminated (although I

 cleaned/replaced them just 40 hours ago) causing enough restriction in

 harsh conditions but not enough to cause a fuel pressure drop at lower

 temps/altitudes. Or I just had a bad batch of fuel.

 I will check the system thoroughly and see if I can find any abnormalities.

 Frans

paul.the.aviator(at)gmail
Guest

Posted: Tue Jul 31, 2012 2:09 pm Post subject: Vapour lock? Why?

Frans, 



Just to clarify.  I have the original pump configuration, two pumps in parallel.  I have an Andair check valve in series with each pump.  Several years after I built my airplane the recommendation was to put the pumps in series.  I did quite a bit of research and I could not come up with a compelling reason to change something that wasn't broken.  With that said, I doubt if the series pump configuration is contributing to your issue.

 

I have a single gascolator on the inlet side and nothing else.  Like Kevin I don't particularly care for a single point of failure, however it would difficult to install a second gascolator now.  If I were to do it over again I would have a gascolator for each pump.

 

Regards, Paul

On Tue, Jul 31, 2012 at 4:27 PM,  <klinefelter.kevin(at)gmail.com (klinefelter.kevin(at)gmail.com)> wrote:

 [quote]--> Europa-List message posted by: klinefelter.kevin(at)gmail.com (klinefelter.kevin(at)gmail.com)

 

 I have an Andair mini gascolator followed by a Y splitting to Andair check valves before the pumps in parallel.

 

 I was chatting with Rob Seaton ( of Rotech in canada) at the Rotax display in Oshkosh. He recently purchased a 914 powered Europa to use as a test vehicle for the 912iS. We were talking about fuel system design, how the new 912iS has two electric pumps like the 914 except higher pressure for the fuel injection. He said he learned how too small a fuel line and/or tortured routing can cause "cavitation" at the pumps.

  I think that's the same thing, cavitation vs vapor lock? So maybe your fuel filter(s), on the suction side of the pump,are causing cavitation in the pump(s). Maybe due to the size (restriction of flow) of the filter, even if they are clean.

  I do not like the fact that I have a single point of failure in one gascolator. But if I redesign, I am going to go with less restriction, larger diameter tubing.

 Kevin

[b]

h&jeuropa

Joined: 07 Nov 2006
Posts: 650

Posted: Tue Jul 31, 2012 4:36 pm Post subject: Re: Vapour lock? Why?

Hi Frans,



We have the same system as you have, the series pumps with check valves as specified by Rotax.  We feed one pump from a Andar gasolator and the other thru a Purolator filter, the one Europa supplied.



Never a problem like you describe in 400 hours.  This summer we have been operating a lot at density altitudes of 12,000 to 18,000 ft using MOGAS with no problem.  Did a trip to Colorado in June and again no problem with MOGAS at 16,000 ft density altitude.  In fact, there is a flight school in Colorado Springs with Flight Design aircraft (912ULS) using exclusively MOGAS.  Colorado Springs is 6000 ft MSL.



So we're pretty confident the problem is not MOGAS.  



Jim & Heather

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